Friday, 24 January 2014

I’ve just finished four months of
intensive ecological fieldwork in the dry forests of Northern Peru. This is the
major fieldwork for my PhD, which aims to develop tools, combining modelling software,
field data and GIS, to provide improved estimates of extinction risk in
threatened Neotropical birds. As part of this, I have surveyed key birds at a
range of sites and I will use these data to assess abundance
and population sizes, and to gauge reactions to habitat change. Most
importantly, I will investigate the relationship between
probability of occurrence for Neotropical birds derived from presence only
niche modelling methods (MAXENT) and bird abundance (densities derived using DISTANCE software). If there is a workable relationship
then the former can be used as a surrogate for the latter in cases where
empirical abundance data are missing.

My study area is part of the
Tumbesian Region, which spans the coasts of Ecuador and northern Peru. It is
part of an Endemic Bird Area, a biodiversity Hotspot, and covers critical
habitat included in WWF’s global 200 ecoregions. The area is important for
conservation due to the high number of endemics, but also due to the threats
faced by the dry forest habitat and its inhabitants - not just birds. Peru has
a burgeoning agricultural export industry, based mainly on the arid coastal
plains, and fed with water from the Andes. This has placed pressure not only on
the dry forest and scrub environments, but also on the traditional goatherding
livelihoods in the region. Many communities are facing difficult choices as to
whether to sell community land for large-scale agriculture, or continue with
the harsh farming lifestyles practiced over the last few hundred years.

Male Peruvian Plantcutter looks
like he has his seat belt on for a rough ride (Photo: Jorge Montejo)

Along with Elio Nuñez, an
undergraduate student at the Universidad Nacional de Piura, I have been
surveying endemic dry forest birds at 26 sites along Peru´s north coast, from
the province of Tumbes, south through Piura and Lambayeque, where the majority
of my field sites are concentrated, south to Ancash. Between June and September
2013, we walked 10 km of transects at each site, once for birds, and once to
measure basic habitat variables. Birds under study include the Endangered
Peruvian Plantcutter Phytotoma raimondii
and Rufous Flycatcher Myiarchus semirufus,
plus 18 other species, seven of which are restricted to Peru.

Sechuran Fox Lycalopex sechurae. Photo:
Christian Devenish

I had two basic requirements in
my study design, I wanted to get a spread of sites across the ranges of my
species (all Tumbesian endemics with relatively restricted ranges), but also
ensure that I would have a fair chance of obtaining data on them, especially
the rarer ones. Given the large size of my whole study area, a random
assignment of sites would not have been feasible. Therefore, I made
distribution models using MAXENT for four species (two rare and two common
sharing very similar ranges), summed the results and sampled sites from
quantiles above a presence/absence threshold, with a heavier weighting for the
top quantile (Figure 1). To ensure good geographic coverage, I created a 25 km
grid over the study area, and repeated the sampling until at least one point fell
within each of 10 cells with the highest average model scores (below in in blue).

Preliminary
results are
interesting. For example, there is a distinct distribution pattern for
both the plantcutter and the Rufous Flycatcher, echoing two of
Rabinowitz’s seven forms
of rarity, on the one hand the plantcutter can be very abundant locally,
but is
very patchily distributed (it was only recorded at half the study sites,
but
reached encounter rates up to a staggering 12 individuals per km). On
the other
hand, the Rufous Flycatcher was widely distributed, but at very low
abundances
(recorded at all but three sites, but only reaching an encounter rate
higher than 1
ind/km at one site).

A very preliminary look at encounter rates against
predicted probability of occurrence (above) from the MAXENT modelsshows a weak, but significant relationship
for two of the more common species (Grey and White Tyrannulet Pseudelaenia leucospodia and Cinereous
Finch Piezorhina cinerea), but not
for both the Peruvian Plantcutter and Rufous Flycatcher. It may well be that there
are other factors behind the rarity of these two species that determine their
distribution, such as much more specific habitat requirements than are
currently represented in the model?With
habitat and land use data from each site, I hope to answer questions like these
in my PhD.

Photo:
Christian Devenish

Christian’s PhD is being
supervised by Stu, along with Graham Smith at MMU, and Graeme Buchanan of RSPB. The Conservation
and Research Fund, The Birdfair/RSPB Research Fund for Endangered Birds and
IdeaWild provided funding for the field project and equipment, and
CONDESAN kindly allowed a flexible working arrangement during the field work.

About the Research Group and blog

This blog includes posts by members of Stuart Marsden's conservation research group based in the School of Science & the Environment at Manchester Metropolitan University. The group mainly includes PhD students working on the conservation ecology of birds and other wildlife, often in the tropics. We also have posts from other collaborators and alumni.